1. Field of the Invention
This invention relates to novel crystalline metal organosilicates and to methods for their preparation and to organic compound conversion, especially hydrocarbon conversion therewith.
2. Description of the Prior Art
Zeolitic materials, both natural and synthetic, have been known in the past to have catalytic capability for various types of hydrocarbon conversion reactions. Certain of these zeolitic materials comprising ordered porous crystalline aluminosilicates have a definite crystalline structure, as determined by X-ray diffraction, within which there are a number of small cavities which are interconnected by a number of still smaller channels. These cavities and channels are precisely uniform in size within a specific zeolitic material. Since the dimensions of these pores are such as to accept for adsorption purposes molecules of certain dimensions while rejecting those of larger dimensions, these materials have commonly been known to be "molecular sieves" and are utilized in a variety of ways to take advantage of the adsorptive properties of these compositions.
These molecular sieves include a wide variety of positive ion containing crystalline aluminosilicates, both natural and synthetic. These aluminosilicates can be described as a rigid three-dimensional network of SiO.sub.4 and AlO.sub.4 in which the tetrahedra are cross linked by the sharing of oxygen atoms whereby the ratio of the total aluminum and silicon atoms to oxygen is 1:2. The electrovalence of the tetrahedra containing aluminum is balanced by the inclusion in the crystal of a cation, for example an alkali metal or alkaline earth cation. Thus, a univalent positive sodium cation balances one negatively charged aluminosilicate tetrahedra where an alkaline earth metal cation is employed in the crystal structure of an aluminosilicate, it balances two negatively charged tetrahedra because of its doubly positive valence. One type of cation may be exchanged either entirely or partially by another type of cation utilizing ion exchange techniques in a conventional manner. By means of such cation exchange, it has been possible to vary the size of the pores in a given aluminosilicate by suitable selection of the particular cation. The spaces between the tetrahedra are occupied by moles of water prior to dehydration.
One such group of crystalline aluminosilicates, designated as those of the ZSM-5 type, have been known and are particularly described in U.S. Pat. No. 3,702,886, the disclosure of which is incorporated herein by reference. The ZSM-5-type crystalline aluminosilicates have been prepared, for example, from a solution containing a tetraalkyl ammonium hydroxide, sodium oxide, an oxide of aluminum or gallium, an oxide of silicon or germanium and water and have been found to be characterized by a specific X-ray diffraction pattern.
The above crystalline aluminosilicates, as previously noted, have been characterized by the presence of aluminum and silicon, the total of such atoms to oxygen being 1:2. The amount of alumina present appears directly related to acidity characteristics of the resulting product. A low alumina content has been recognized as being advantageous in attaining a low degree of acidity which in many catalytic reactions is translated into low coke making properties and low aging rates.